Compared with the first-generation semiconductor of silicon and the second-generation semiconductor of GaAs, the semiconductor material of GaN has many advantages such as large band gap, high electron saturation velocity, high breakdown voltage and ability of withstanding high temperatures, which makes it more suitable for electronic devices having high temperature, high pressure, high frequency and high power. Due to the above-mentioned advantages, GaN has broad application prospects and becomes hot research topic in the field of semiconductor industry.
GaN High Electron Mobility Transistor (HEMT) is formed using two-dimensional electron gas at AlGaN/GaN heterojunction and can be applied to the field of high frequency, high voltage and high power. Depletion mode GaN HEMT devices are generally produced using the characteristic of constant opening of a two-dimensional electron gas channel since the two-dimensional electron gas has high mobility and high saturation velocity, and thus are appropriate for high frequency applications in the field of wireless communications. During the packaging process of GaN devices, a structure having through holes is generally used to increase the gain of the devices and reduce grounded inductance. In this structure, etching is generally performed from the rear side of a substrate which is connected to ground to form through holes which penetrate the substrate and the nitride semiconductor epitaxial layer to a source electrode. And then the through holes are filled with metal so that the source electrode is connected to the grounded rear side of the substrate, and thus the inductance from the source electrode to ground is reduced.